According to the 2010 census, the city has a total area of 46.91 square miles (121.5 km2), of which 42.22 square miles (109.3 km2) (or 90.00%) is land and 4.69 square miles (12.1 km2) (or 10.00%) is water.[3] Lakes include Lake Decatur, formed in 1923 by the damming of the Sangamon River.

There were 34,086 households, out of which 27.6% had children under the age of 18 living with them, 44.1% were married couples living together, 14.1% had a female householder with no husband present, and 38.1% were non-families. 32.7% of all households were made up of individuals and 13.0% had someone living alone who was 65 years of age or older. The average household size was 2.30 and the average family size was 2.90.

In the city the population was spread out with 24.0% under the age of 18, 11.1% from ages 18 to 24, 26.0% from ages 25 to 44, 22.5% from ages 45 to 64, and 16.4% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 87.9 males. For every 100 females aged 18 and over, there were 83.9 males.

The median income for a household in the city was $33,111, and the median income for a family was $42,379. Males had a median income of $36,920 versus $22,359 for females. The per capita income for the city was $19,009. About 12.1% of families and 16.5% of the population were below the poverty line, including 25.1% of those under age 18 and 9.0% of those age 65 or over.

The city's symbol is the Transfer House, an early-20th-century Victorian structure located originally in the center of town where the city's mass transit lines met. The Transfer House was moved in 1963 to save it from possible destruction as increasing automobile traffic flowed through the highway routed through downtown.

Since 1966, Decatur has been Sister Citied with Tokorozawa, Saitama, Japan. In July 1972, the administrations of 19 independent smaller municipalities were merged to form Decatur's second Sister City, Seevetal, Lower Saxony, Germany. The 19 towns and villages forming Seevetal were Beckedorf, Bullenhausen, Emmelndorf, Fleestedt, Glüsingen, Groß Moor, Helmstorf, Hittfeld, Holtorfsloh, Horst, Hörsten, Klein Moor, Lindhorst, Maschen, Meckelfeld, Metzendorf, Ohlendorf, Over and Ramelsloh. The Decatur Sister Cities Committee annually coordinates both inbound and outbound High School students, who serve as ambassadors between the three cities. Since mid-2012, the City of Decatur and City of Camajuaní in the Province of Villa Clara, Cuba have worked to develop Sister City relations. As of March 2013, both governments have approved the relationship, but no formal agreements have been signed.[10]

Between 1829 and 1836 the county commissioners court had jurisdiction as it was the seat of Macon County,.[11][12] By 1836 the population reached approximately 300, Richard Oglesby was elected president of the first board of trustees.[11] Other members of the board of trustees included Dr. William Crissey, H.M. Gorin and Andrew Love as clerk,.[11][12]

In 1839 a town charter was granted to Decatur that gave power to the trustees "to establish and regulate a fire department, to dig wells and erect pumps in the streets, regulate police of the town, raise money for the purpose of commencing and prosecuting works of public improvement.",.[11][12] Those who served as president of the town of Decatur were: Richard Oglesby (1836), Joseph Williams (1837), Henry Snyder (1838), Kirby Benedict (1839), Joseph King (1840), Thomas P. Rodgers (1841), David Crone (1846–47), J.H. Elliott (1848), Joseph Kauffman (1849), Joseph King (1850), William S. Crissey (1851), W.J. Stamper (1852), William Prather (1853–54), and Thomas H. Wingate (1854–55).[11]

In the winter of 1855-56, a special city incorporation charter was obtained.[11][12] This charter provided an aldermanic form of government and on January 7, 1856 an election was held for mayor, two aldermen for each of the four wards, and city marshall.[11][12] This aldermanic form of government continued until January 18, 1911 when Decatur changed to city commissioner form of government.[11][13] The new commissioner system provided a mayor elected at large and four commissioners to serve as administrators of city services: accounts and finance, public health and safety, public property, and streets and public improvements. The mayor also served as Commissioner of Public Affairs,.[13][14]

The mayor and commissioner system prevailed until a special election on November 25, 1958 in which the present council-manager form of government was adopted.[12][14] According to the city website, the "City of Decatur operates under the Council-Manager form of government, a system which combines the leadership of a representative, elected council with the professional background of an appointed manager."[15] The mayor and all members of the council are elected at large. Their duties include determining city policy, receiving nominal annual salaries, and as representatives of the city in public ceremonies.[16] The appointed manager handles all city administration and is the council's employee and not an elected official.[14] Since 1959, the following have served as City Managers: John E. Dever, W. Robert Semple, Leslie T. Allen, Jim Bacon, Jim Williams, Steve Garman, John A. Smith (acting), Ryan McCrady, Gregg Zientara (interim), and Timothy Gleason. [17]

The Decatur Transfer House in the background in downtown's Central Park

As of 2014[update], The current mayor of Decatur is Mike McElroy, a former councilman and local business executive.[18] McElroy was originally elected in April 2009 to finish the term of former mayor Paul Osborne. He works for a liquor distribution company and therefore defers the responsibility of liquor commissioner normally held by the mayor.[19] In April 2011, McElroy ran unopposed for a full term as mayor.[20] Timothy Gleason has served as city manager of Decatur since March 23, 2015.[21]

The Muni band was organized September 19, 1857 making it one of the oldest nonmilitary bands in continuous service in the United States and Canada.[24] It was originally known as the Decatur Brass Band, Decatur Comet Band and the Decatur Silver Band until 1871 when it was reorganized by Andrew Goodman and became the Goodman Band. In 1942 it was officially designated as the Decatur Municipal Band.

The Decatur Public Library was originally built with a grant from Andrew Carnegie. The original library was built in 1902 and opened to the public in 1903. The building served the community until 1970 when the library moved to North Street at the site of a former Sears, Roebuck & Co. store. In 1999 the library moved to its present location on Franklin Street, which is also an abandoned Sears building. The library is part of the Illinois Heartland Library System.[25] Decatur is one of only a very few communities to have razed an original Carnegie Library. A bank now stands in its place.

From 1900 to 1974, Decatur was the home of the Commodores, a minor-league baseball team playing at Fans Field.

The USTA/Ursula Beck Pro Tennis Classic has been held annually since 1999. Male players from over 20 countries compete for $10,000 in prize money as well as ATP world ranking points at the Fairview Park Tennis Complex. The tournament is held for ten consecutive days at Fairview Park concluding on the first weekend in August.

The Decatur High School [later Stephen Decatur H. S.] "Reds"/"Runnin' Reds" won the Illinois High School Association (IHSA) State Basketball Championship in 1931, 1936, 1945, and 1962. In addition, they were 2nd in 1937; 3rd in 1964; and 4th in 1912, 1951, 1960, and 1966. For many years they held the overall record for appearances in the "Sweet 16" and the "Elite 8." They were consistently one of the premier high school basketball teams in America. Legendary coach Galen Kintner was at the helm for the first three titles.[29]

Caterpillar Inc. has one of its largest manufacturing plants in the U.S. This plant produces Caterpillar's off highway trucks, wheel-tractor scrapers, mining-class motorgraders, and their ultra-class mining trucks (including the Caterpillar 797). Archer Daniels Midland processes corn and soybeans, Mueller produces water distribution products and Tate & Lyle processes corn in Decatur. From 1917-1922 Decatur was the location of the Comet Automobile Co.,[33] and the Pan-American Motor Corp.

The Decatur Public Transit System (DPTS) provides fixed route bus service as well as complementary door-to-door paratransit service for people with disabilites, who are unable to use the bus system, throughout the City of Decatur. Under an agreement with the Village of Forsyth, service is also provided to the Hickory Point Mall area in Forsyth.

Trolley transfer station in its original location at the intersection of Main and Main streets; from a postcard sent in 1906

Statue of Abraham Lincoln in downtown Decatur on the site of his first political speech. The plaque reads “Abraham Lincoln’s first political speech: Lincoln mounted a stump by Harrell’s Tavern facing this square and defended the Illinois Whig party candidates near this spot at age 21 in the summer of 1830”

Decatur was the first home in Illinois of Abraham Lincoln, who settled just west of Decatur with his family in 1830. At the age of 21, Lincoln gave his first political speech in Decatur about the importance of Sangamon River navigation that caught the attention of Illinois political leaders.[citation needed] As a lawyer on the 8th Judicial Circuit, Lincoln made frequent stops in Decatur, and argued five cases in the log courthouse that stood on the corner of Main & Main Streets. The original courthouse is now on the grounds of the Macon County Historical Museum on North Fork Road.[citation needed]

On May 9 and 10, 1860, the Illinois Republican State Convention was held in Decatur. At this convention Lincoln received his first endorsement for President of the United States as "The Railsplitter Candidate." In commemoration of Lincoln's bicentennial the Illinois Republican State Convention was held in Decatur at the Decatur Conference Center and Hotel on June 6 & 7, 2008.[49]

The lysine conspirators, including ADM, ultimately settled federal charges for more than $100 million. ADM also paid hundreds of millions of dollars [$400 million alone on the high fructose corn syrup Class Action case] to plaintiffs/customers that it stole from during the price-fixing schemes.[50][51][52][53] Furthermore, several Asian and European lysine and citric acid producers, that conspired to fix prices with ADM, paid criminal fines in the tens of millions of dollars to the U.S. government.[54] Several executives, including the Vice Chairman of ADM, did federal prison time.

The investigation and prosecution of ADM and some of its executives has been reported to be one of the "best documented corporate crimes in American history".[55] The events were the basis of a book named The Informant as well as a film named The Informant!

In 2013, ADM reported that some employees had violated the Foreign Corrupt Practices Act, and ADM was fined 14 million U.S. dollars, but avoided criminal charges by self-reporting the foreign bribes.

In 2014, ADM moved its upper corporate management out of Decatur and established the new ADM World Headquarters in downtown Chicago.

On April 18 and 19, 1996, the city was hit by tornadoes. On April 18, an F1 tornado hit the city's southeast side, followed by an F3 tornado the following evening on the northwest side. The two storms totaled approximately $10.5 million in property damage.[56]

On July 19, 1974 a tanker car containing isobutane collided with a boxcar in the Norfolk & Western railroad yard in the East End of Decatur. The resulting explosion killed seven people, injured 349, and caused $18 million in property damage.[57]

In November 1999, Decatur was brought into the national news when the Rev. Jesse Jackson and the Rainbow/PUSH Coalition protested the expulsion and treatment of several African American students who had been involved in a serious fight at an Eisenhower High School football game.[58]

"Decatur, Or, Round of Applause For Your Step Mother!" is a song by Sufjan Stevens on his album Illinois. The song refers to several locations and events associated with Decatur, including the Caterpillar factory, Greenwood cemetery, the chicken mobile from Krekel's, strong historical ties to Abraham Lincoln, and the Sangamon River.[61]

Canadian folk singer Willie P. Bennett wrote a song titled "Hearts in Decatur" which he performed live but never recorded.[62]

In the 2008 film Leatherheads starring George Clooney, there is a scene where a man and woman are sitting in the stands at a football game. The woman asks "how owning a football team will help sell corn starch?", then the camera pans the scoreboard and reveals that one of the teams is Decatur.